This invention relates to an escape device installed on an aircraft for use as an escape slide or a life-saving raft in case of an emergency such as an emergency landing.
Unexamined Japanese Patent Publication 59-152851 discloses an escape device for an aircraft of this type. It is normally stored in the aircraft in a folded state. In case of emergency, it is inflated by blowing gas thereinto to form a slide.
As shown in FIG. 1, this device comprises an opposed pair of cylindrical gas bags 1 formed by bonding flexible sheets together, and a sheet member provided between and secured to the gas bags 1. Its top surface serves as a slide surface 2. By inflating the gas bags 1 by blowing gas thereinto, this device can be used as a slide. In case the aircraft has landed on the sea, it can also be used as a life raft by detaching it from the aircraft, because the gas bags 1 have buoyancy.
It is required that sheet members 3 and 4, forming the gas bags 1 and the sliding surface 2 of the escape device, be foldable to a sufficiently small size and inflatable to a fairly large size.
When using the device as a slide, the gas bags 1 serve to hold the shape of the slide. Thus, they have to have a sufficient rigidity. If the device is used as a life raft, the bags serve as floats for keeping the raft afloat on the water. It is therefore essential that the joint portions of the sheets forming the gas bags stably exhibit a high bond strength and high air-tightness.
If a fire breaks out in an emergency situation, the escape device will be exposed to very high radiation heat. The joint portions of the sheets forming the gas bags are thus required to maintain their high bond strength even under high-temperature conditions. There is also the possibility that the escape device might catch fire. Thus, in order to prevent the sheet members 3 and 4 from burning, they are required to have a sufficient flame retardancy.
Also, in order that the sheet member forming the slide surface may not be torn apart from surface scratches that may be formed when passengers slide down, it has to be made of a material having a sufficient tear resistance.
To meet these requirements, as shown in FIG. 11, Unexamined Japanese Patent Publication 59-152851 proposes an escape device in which the sheet members 3 and 4 forming the gas bags and slide surface are in the form of a rubber coated fabric comprising a flexible substrate 41 made from a nylon fabric or the like and covering layers 42 and 43 of elastomers made from a thermoplastic polymer to give the sheet members sufficient strength and elasticity to be foldable and deformable when expanded.
The thermoplastic polymer forming the covering layers 42 and 43 contain various fillers for improved flame retardancy.
Such a rubber coated fabric comprising the substrate 41 and the elastomeric covering layers 42 and 43 has to be strongly bonded between its substrate and covering layers so that they will not peel off from each other when passengers slide down thereon. It was an ordinary practice to bond the covering layers 42 and 43 to the substrate 41 through an adhesive applied to both sides of the substrate to improve the bond strength between the substrate 41 and covering layers 42 and 43.
The adhesive applied to the substrate improves the bond strength between the covering layers and the substrate. But it also tends to harden the rubber coated fabric, thus lowering its tear strength.
One way to increase the flame retardancy of the rubber coated fabric is to improve the self-extinguishing properties of the covering layers 42 and 43 by adding flame-retardants to the elastomer forming the covering layers. But if the added flame-retardants are not dispersed uniformly, the flame resistance may decrease drastically, so that the rubber coated fabric is more likely to easily catch fire and burn.
Moreover, since the covering layers 42 and 43 of the sheet member 3 are made from a thermoplastic polymer, if exposed to radiation heat, the thermoplastic polymer itself may soften by heat. This lowers its strength. If exposed to high-temperature radiation heat, the thermoplastic polymer may melt and increase its fluidity. Since the gas pressure in the gas bags rises when heated, the covering layers of thermoplastic polymer may be pushed outwards. In an extreme case, the sheet member 3 may be broken. Air-tightness is lost if this happens.
Also, if the thermoplastic polymer forming the covering layers 42 and 43 contains fillers which shrink and stretch to different degrees than the polymer, if the sheet member 3 forming each gas bag 3 is stretched by the inner pressure, gaps may be formed between the polymer and the fillers because they are stretched to different degrees from each other. Such gaps can impair the air-tightness.